Insights into the role of elastin in vocal fold health and disease

Elastin-derived peptides (EDPs) affect gene and protein expression in human mesenchymal stem cells (hMSCs) - preliminary study

During the aging process, elastin is degraded and the level of elastin-derived peptides (EDPs) successively increases. The main peptide released from elastin during its degradation is a peptide with the VGVAPG sequence. To date, several papers have described that EDPs or elastin-like peptides (ELPs) affect human mesenchymal stem cells (hMSCs) derived from different tissues. Unfortunately, despite the described effect of EDPs or ELPs on the hMSC differentiation process, the mechanism of action of these peptides has not been elucidated. Therefore, the aim of the present study was to evaluate the impact of the VGVAPG and VVGPGA peptides on the hMSC stemness marker and elucidation of the mechanism of action of these peptides. Our data show that both studied peptides (VGVAPG and VVGPGA) act with the involvement of ERK1/2 and c-SRC kinases. However, their mechanism of activation is probably different in hMSCs derived from adipose tissue. Both studied peptides increase the KI67 protein level in hMSCs, but this is not accompanied with cell proliferation. Moreover, the changes in the NANOG and c-MYC protein expression and in the SOX2 and POU5F1 mRNA expression suggest that EDPs reduced the hMSC stemness properties and could initiate cell differentiation. The initiation of differentiation was evidenced by changes in the expression of AhR and PPARγ protein as well as specific genes (ACTB, TUBB3) and proteins (β-actin, RhoA) involved in cytoskeleton remodeling. Our data suggest that the presence of EDPs in tissue can initiate hMSC differentiation into more tissue-specific cells.

Localized delivery of therapeutics impact laryngeal mechanics, local inflammatory response, and respiratory microbiome following upper airway intubation injury in swine

BACKGROUND

Laryngeal injury associated with traumatic or prolonged intubation may lead to voice, swallow, and airway complications. The interplay between inflammation and microbial population shifts induced by intubation may relate to clinical outcomes. The objective of this study was to investigate laryngeal mechanics, tissue inflammatory response, and local microbiome changes with laryngotracheal injury and localized delivery of therapeutics via drug-eluting endotracheal tube.

METHODS

A simulated traumatic intubation injury was created in Yorkshire crossbreed swine under direct laryngoscopy. Endotracheal tubes electrospun with roxadustat or valacyclovir- loaded polycaprolactone (PCL) fibers were placed in the injured airway for 3, 7, or 14 days (n = 3 per group/time and ETT type). Vocal fold stiffness was then evaluated with normal indentation and laryngeal tissue sections were histologically examined. Immunohistochemistry and inflammatory marker profiling were conducted to evaluate the inflammatory response associated with injury and ETT placement. Additionally, ETT biofilm formation was visualized using scanning electron microscopy and micro-computed tomography, while changes in the airway microbiome were profiled through 16S rRNA sequencing.

RESULTS

Laryngeal tissue with roxadustat ETT placement had increasing localized stiffness outcomes over time and histological assessment indicated minimal epithelial ulceration and fibrosis, while inflammation remained severe across all timepoints. In contrast, vocal fold tissue with valacyclovir ETT placement showed no significant changes in stiffness over time; histological analysis presented a reduction in epithelial ulceration and inflammation scores along with increased fibrosis observed at 14 days. Immunohistochemistry revealed a decline in M1 and M2 macrophage markers over time for both ETT types. Among the cytokines, IL-8 levels differed significantly between the roxadustat and valacyclovir ETT groups, while no other cytokines showed statistically significant differences. Additionally, increased biofilm formation was observed in the coated ETTs with notable alterations in microbiota distinctive to each ETT type and across time.

CONCLUSION

The injured and intubated airway resulted in increased laryngeal stiffness. Local inflammation and the type of therapeutic administered impacted the bacterial composition within the upper respiratory microbiome, which in turn mediated local tissue healing and recovery.

High-Resolution Profiling of Human Vocal Fold Cellular Landscapes With Single-Nuclei RNA Sequencing

INTRODUCTION

The function of the vocal folds (VFs) is determined by the phenotype, abundance, and distribution of differentiated cells within specific microenvironments. Identifying this histologic framework is crucial in understanding laryngeal disease. A paucity of studies investigating VF cellular heterogeneity has been undertaken. Here, we examined the cellular landscape of human VFs by utilizing single-nuclei RNA-sequencing.

METHODS

Normal true VF tissue was excised from five patients undergoing pitch elevation surgery. Tissue was snap frozen in liquid nitrogen and subjected to cellular digestion and nuclear extraction. Nuclei were processed for single-nucleus sequencing using the 10X Genomics Chromium platform. Sequencing reads were assembled using cellranger and analyzed with the scanpy package in python.

RESULTS

RNA sequencing revealed 18 global cell clusters. While many were of epithelial origin, expected cell types, such as fibroblasts, immune cells, muscle cells, and endothelial cells were present. Subcluster analysis defined unique epithelial, immune, and fibroblast subpopulations.

CONCLUSION

This study evaluated the cellular heterogeneity of normal human VFs by utilizing single-nuclei RNA-sequencing. With further confirmation through additional spatial sequencing and microscopic imaging, a novel cellular map of the VFs may provide insight into new cellular targets for VF disease.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:3193-3200, 2024.

Identification of Smith-Magenis syndrome cases through an experimental evaluation of machine learning methods

This research work introduces a novel, nonintrusive method for the automatic identification of Smith-Magenis syndrome, traditionally studied through genetic markers. The method utilizes cepstral peak prominence and various machine learning techniques, relying on a single metric computed by the research group. The performance of these techniques is evaluated across two case studies, each employing a unique data preprocessing approach. A proprietary data "windowing" technique is also developed to derive a more representative dataset. To address class imbalance in the dataset, the synthetic minority oversampling technique (SMOTE) is applied for data augmentation. The application of these preprocessing techniques has yielded promising results from a limited initial dataset. The study concludes that the k-nearest neighbors and linear discriminant analysis perform best, and that cepstral peak prominence is a promising measure for identifying Smith-Magenis syndrome.

Neural network-based estimation of biomechanical vocal fold parameters

Vocal fold (VF) vibrations are the primary source of human phonation. High-speed video (HSV) endoscopy enables the computation of descriptive VF parameters for assessment of physiological properties of laryngeal dynamics, i.e., the vibration of the VFs. However, underlying biomechanical factors responsible for physiological and disordered VF vibrations cannot be accessed. In contrast, physically based numerical VF models reveal insights into the organ's oscillations, which remain inaccessible through endoscopy. To estimate biomechanical properties, previous research has fitted subglottal pressure-driven mass-spring-damper systems, as inverse problem to the HSV-recorded VF trajectories, by global optimization of the numerical model. A neural network trained on the numerical model may be used as a substitute for computationally expensive optimization, yielding a fast evaluating surrogate of the biomechanical inverse problem. This paper proposes a convolutional recurrent neural network (CRNN)-based architecture trained on regression of a physiological-based biomechanical six-mass model (6 MM). To compare with previous research, the underlying biomechanical factor "subglottal pressure" prediction was tested against 288 HSV ex vivo porcine recordings. The contributions of this work are two-fold: first, the presented CRNN with the 6 MM handles multiple trajectories along the VFs, which allows for investigations on local changes in VF characteristics. Second, the network was trained to reproduce further important biomechanical model parameters like VF mass and stiffness on synthetic data. Unlike in a previous work, the network in this study is therefore an entire surrogate of the inverse problem, which allowed for explicit computation of the fitted model using our approach. The presented approach achieves a best-case mean absolute error (MAE) of 133 Pa (13.9%) in subglottal pressure prediction with 76.6% correlation on experimental data and a re-estimated fundamental frequency MAE of 15.9 Hz (9.9%). In-detail training analysis revealed subglottal pressure as the most learnable parameter. With the physiological-based model design and advances in fast parameter prediction, this work is a next step in biomechanical VF model fitting and the estimation of laryngeal kinematics.

Exploring the anti-inflammatory potential of topical hyaluronic acid for vocal fold injury in a rat model

PURPOSE

Vocal fold injuries are associated with fibrosis and dysphonia, which is a major obstacle to surgical treatment. The aim of this study is to evaluate the effect of topical hyaluronic acid with or without diclofenac on the inflammatory phase of vocal fold wound healing.

METHODS

Forty-one male Sprague-Dawley rats were randomly assigned to four groups: an uninjured control group, an injured control group without any treatment, and two intervention groups in which hyaluronic acid with or without diclofenac was applied to the injured vocal fold. Gene expression of inflammatory markers and ECM-related molecules were examined.

RESULTS

Vocal fold injury resulted in a significant upregulation of inflammatory parameters [Ptgs2, Il1b and Il10] and Has1. Tgfb1, Has3 and Eln gene expression were significantly downregulated by the topical application of hyaluronic acid. The combination of hyaluronic acid and diclofenac did not result in any significant changes.

CONCLUSIONS

Vocal fold wound healing was significantly improved by a single post-operative topical application of hyaluronic acid. The addition of diclofenac may provide no additional benefit.

Improved tropoelastin synthesis in the skin by codon optimization and nucleotide modification of tropoelastin-encoding synthetic mRNA

Loss of elastin due to aging, disease, or injury can lead to impaired tissue function. In this study, de novo tropoelastin (TE) synthesis is investigated in vitro and in vivo using different TE-encoding synthetic mRNA variants after codon optimization and nucleotide modification. Codon optimization shows a strong effect on protein synthesis without affecting cell viability in vitro, whereas nucleotide modifications strongly modulate translation and reduce cell toxicity. Selected TE mRNA variants (3, 10, and 30 μg) are then analyzed in vivo in porcine skin after intradermal application. Administration of 30 μg of native TE mRNA with a me1 Ψ modification or 10 and 30 μg of unmodified codon-optimized TE mRNA is required to increase TE protein expression in vivo. In contrast, just 3 μg of a codon-optimized TE mRNA variant with the me1 Ψ modification is able to increase protein expression. Furthermore, skin toxicity is investigated in vitro by injecting 30 μg of mRNA of selected TE mRNA variants into a human full-thickness skin model, and no toxic effects are observed. Thereby, for the first time, an increased dermal TE synthesis by exogenous administration of synthetic mRNA is demonstrated in vivo. Codon optimization of a synthetic mRNA can significantly increase protein expression and therapeutic outcome.

Sequence variants affecting voice pitch in humans

The genetic basis of the human vocal system is largely unknown, as are the sequence variants that give rise to individual differences in voice and speech. Here, we couple data on diversity in the sequence of the genome with voice and vowel acoustics in speech recordings from 12,901 Icelanders. We show how voice pitch and vowel acoustics vary across the life span and correlate with anthropometric, physiological, and cognitive traits. We found that voice pitch and vowel acoustics have a heritable component and discovered correlated common variants in ABCC9 that associate with voice pitch. The ABCC9 variants also associate with adrenal gene expression and cardiovascular traits. By showing that voice and vowel acoustics are influenced by genetics, we have taken important steps toward understanding the genetics and evolution of the human vocal system.

Perirenal adipose tissues as a human elastin source, and optimize the extraction process

Elastin is very rarely repaired extracellular matrix (ECM) in physiological condition. The commercial human elastin for exogenous medical treatment is very expensive, and has a potential for disease transmission. Animal-origin elastin is relatively low price, but has concerns for xenogeneic immune responses. Considering cost and safety, we focused on the perirenal adipose tissue, donated from healthy young people via donor nephrectomy. Until now, all of the perirenal adipose tissues are discarded as a medical waste after kidney transplantation. In the present study, we applied perirenal adipose tissues as the source of human elastin, and optimized the extraction process to get high purified and quantified elastin. Through pre-processing step, the delipidated and decellularized ECM was prepared. Next, with four different elastin extraction process (acidic solvents, neutral salt, organic solvents or hot alkali method), elastin was extracted, and the concentration of amino acid between each product was compared, and bright-field/electron microscopy, Fourier transform infrared (FT-IR) spectroscopy and cytotoxicity analysis were also performed. As controls, bovine neck ligament-derived and human skin-derived elastin were used. Among the elastin extraction methods, the hot alkali insoluble product showed (1) relatively high positive area of Verhoeff's and low Masson's trichrome stain, (2) 64.24% purity, 159.29 mg/g quantity, and ∼6.37% yield in amino acid analysis, (3) β-sheet second structure, and (4) thin fiber composed mesh-like sheet structure in SEM image. These values were higher than those of the commercial human skin elastin. When comparing hydrolyzed forms, α-elastin from hot alkali insoluble product showed enhanced cell proliferation and maintained cell properties compared to the κ-elastin. Therefore, we confirmed that the perirenal adipose tissue is an ideal source of human elastin with safety assurance, and the hot alkali process combined with pre-process seems to be the optimal method for elastin extraction with high purity and quantity.

The role of systemic dehydration in vocal fold healing: Preliminary findings

Rationale

Systemic dehydration negatively alters the expression of vocal fold inflammatory and cell junction markers. These biological changes can have downstream effects on the healing processes of injured vocal folds. In the dermis, reduced hydration prolongs inflammation and delays healing. It is unknown whether this biological effect is observed in vocal fold tissue.

Objective

To investigate the effects of systemic dehydration on vocal fold healing outcomes following acute, bilateral vocal fold injury in a rodent model.

Methods

Eighteen systemic dehydrated and 18 euhydrated adult male Sprague Dawley rats experienced bilateral vocal fold injuries or no injury (N = 9/group). Vocal fold gene expression levels of inflammatory mediators and epithelial cell junction markers were measured 24 h post-injury.

Results

Pro-inflammatory gene markers (IL-1β; TNF-α) were differentially expressed in response to systemic dehydration with vocal fold injury compared to non-injury. Epithelial cell junction markers (Cadherin-3, Desmoglein-1) also exhibited divergent trends following systemic dehydration, but these data were not statistically significant.

Conclusions

Systemic dehydration may affect cellular vocal fold healing processes within 24 h. These findings lay the groundwork for further investigation of how hydration status can affect vocal fold tissue recovery and influence clinical care.

Tissue Engineering as a Promising Treatment for Glottic Insufficiency: A Review on Biomolecules and Cell-Laden Hydrogel

Glottic insufficiency is widespread in the elderly population and occurs as a result of secondary damage or systemic disease. Tissue engineering is a viable treatment for glottic insufficiency since it aims to restore damaged nerve tissue and revitalize aging muscle. After injection into the biological system, injectable biomaterial delivers cost- and time-effectiveness while acting as a protective shield for cells and biomolecules. This article focuses on injectable biomaterials that transport cells and biomolecules in regenerated tissue, particularly adipose, muscle, and nerve tissue. We propose Wharton's Jelly mesenchymal stem cells (WJMSCs), induced pluripotent stem cells (IP-SCs), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), insulin growth factor-1 (IGF-1) and extracellular vesicle (EV) as potential cells and macromolecules to be included into biomaterials, with some particular testing to support them as a promising translational medicine for vocal fold regeneration.

Prevalence and Determinants of Hoarseness in School-Aged Children

Hoarseness in school-aged children may affect their educational achievement and interfere with their communication and social skills development. The global prevalence of hoarseness in school-aged children ranges between 6% and 23%. To the best of our knowledge, there is a scarcity of studies describing the prevalence or determinates of hoarseness in Saudi school-aged children. Our aim was to measure the prevalence of hoarseness among school-aged children and to identify its determinants. A cross-sectional questionnaire-based survey was used that included randomly selected primary and early childhood schools from private and governmental sectors in Saudi Arabia. The data were collected using a questionnaire which was self-completed by the children's parents and covered the following aspects: sociodemographic features, health and its related comorbidities about children and their families, attendance and performance in school, child's voice tone, past history of frequent crying during infancy, history of letter pronunciation problems and stuttering, the Reflux Symptom Index (RSI) and the Children's Voice Handicap Index-10 for parents (CVHI-10-P). Determinants of hoarseness were investigated using the SPSS software (version 20). The mean age of the study children (n = 428) was 9.05 years (SD = 2.15), and 69.40% of them were male. The rate of hoarseness in the participants was 7.5%. Hoarseness was significantly common in children with a history of excessive infancy crying (p = 0.006), letter pronunciation issues (especially 'R' and 'S'; p = 0.003), and stuttering (p = 0.004) and in those with a previous history of hoarseness (p = 0.023). In addition, having the symptoms of gastrointestinal reflux increased the risk of hoarseness by four times (OR = 4.77, 95% CI = 2.171, 10.51). In summary, hoarseness in children may be dangerously underestimated, as it may reflect the presence of speech problems, in addition to the presence of laryngopharyngeal reflux (LPR). Hoarseness was assumed on the basis of parental complaints. Therefore, further research with diagnoses based on a clinical assessment is needed to understand the magnitude of the hoarseness problem and its consequences in children.

Bioreactors for Vocal Fold Tissue Engineering

It is estimated that almost one-third of the United States population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability are presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of proinflammatory and profibrotic genes in vitro. Although the precision and accuracy of bioreactors contribute to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies. Impact statement We present a comprehensive review of bioreactors for vocal fold (VF) tissue engineering with a focus on the influence of the phonatory environment on the development, function, injury, and healing of the VFs and the importance of mimicking phonation on engineered VF tissues in vitro. Furthermore, we put forward a strong argument for the continued development of bioreactors in this area with an emphasis on the standardization of bioreactor designs, principles, operating parameters, and oscillatory regimes to enable comparisons between studies.

Human amniotic epithelial cell transplantation improves scar remodeling in a rabbit model of acute vocal fold injury: a pilot study

Objective

To gain insight into the molecular mechanisms underlying the early stages of vocal fold extracellular matrix (ECM) remodeling after a mid-membranous injury resulting from the use of human amniotic epithelial cells (hAEC), as a novel regenerative medicine cell-based therapy.

Methods

Vocal folds of six female, New Zealand White rabbits were bilaterally injured. Three rabbits had immediate bilateral direct injection of 1 × 10⁶ hAEC in 100 µl of saline solution (hAEC) and three with 100 µl of saline solution (controls, CTR). Rabbits were euthanized 6 weeks after injury. Proteomic analyses (in-gel trypsin protein digestion, LC–MS/MS, protein identification using Proteome Discoverer and the Uniprot Oryctolagus cuniculus (Rabbit) proteome) and histological analyses were performed.

Results

hAEC treatment significantly increased the expression of ECM proteins, elastin microfibril interface-located protein 1 (EMILIN-1) and myocilin that are primarily involved in elastogenesis of blood vessels and granulation tissue. A reactome pathway analysis showed increased activity of the anchoring fibril formation by collagen I and laminin, providing mechanical stability and activation of cell signaling pathways regulating cell function. hAEC increased the abundance of keratin 1 indicating accelerated induction of the differentiation programming of the basal epithelial cells and, thereby, improved barrier function. Lastly, upregulation of Rab GDP dissociation inhibitor indicates that hAEC activate the vesicle endocytic and exocytic pathways, supporting the exosome-mediated activation of cell–matrix and cell-to-cell interactions.

Conclusions

This pilot study suggests that injection of hAEC into an injured rabbit vocal fold favorably alters ECM composition creating a microenvironment that accelerates differentiation of regenerated epithelium and promotes stabilization of new blood vessels indicative of accelerated and improved repair.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02701-w.

Prediction of subcutaneous drug absorption - do we have reliable data to design a simulated interstitial fluid?

For many years subcutaneous (SC) administration has represented the main route for delivering biopharmaceuticals. However, little information exists about the milieu in the subcutaneous tissue, especially about the properties/composition of the fluid present in this tissue, the interstitial fluid (ISF), which is one of the key elements for the drug release and absorption. Better knowledge on SC ISF composition, properties and dynamics may provide better insight into in vivo drug performance. In addition, a simulated SC ISF, which allows better prediction of in vivo absorption of drugs after subcutaneous administration based on in vitro release experiments, would help to improve formulation design, and reduce the number of animal studies and clinical trials required to obtain marketing authorization. To date, a universal medium for predicting drug solubility/release in the interstitial space does not exist. This review provides an overview of the currently available information on composition and physicochemical properties of SC ISF and critically discusses different isolation techniques in the context of information that could be gained from the isolated fluid. Moreover, it surveys current in vitro release media aiming to mimic SC ISF composition and highlights information gaps that need to be filled for designing a meaningful artificial SC ISF.

Roars, groans and moans: Anatomical correlates of vocal diversity in polygynous deer

Eurasian deer are characterized by the extraordinary diversity of their vocal repertoires. Male sexual calls range from roars with relatively low fundamental frequency (hereafter fo ) in red deer Cervus elaphus, to moans with extremely high fo in sika deer Cervus nippon, and almost infrasonic groans with exceptionally low fo in fallow deer Dama dama. Moreover, while both red and fallow males are capable of lowering their formant frequencies during their calls, sika males appear to lack this ability. Female contact calls are also characterized by relatively less pronounced, yet strong interspecific differences. The aim of this study is to examine the anatomical bases of these inter-specific and inter-sexual differences by identifying if the acoustic variation is reflected in corresponding anatomical variation. To do this, we investigated the vocal anatomy of male and female specimens of each of these three species. Across species and sexes, we find that the observed acoustic variability is indeed related to expected corresponding anatomical differences, based on the source-filter theory of vocal production. At the source level, low fo is associated with larger vocal folds, whereas high fo is associated with smaller vocal folds: sika deer have the smallest vocal folds and male fallow deer the largest. Red and sika deer vocal folds do not appear to be sexually dimorphic, while fallow deer exhibit strong sexual dimorphism (after correcting for body size differences). At the filter level, the variability in formants is related to the configuration of the vocal tract: in fallow and red deer, both sexes have evolved a permanently descended larynx (with a resting position of the larynx much lower in males than in females). Both sexes also have the potential for momentary, call-synchronous vocal tract elongation, again more pronounced in males than in females. In contrast, the resting position of the larynx is high in both sexes of sika deer and the potential for further active vocal tract elongation is virtually absent in both sexes. Anatomical evidence suggests an evolutionary reversal in larynx position within sika deer, that is, a secondary larynx ascent. Together, our observations confirm that the observed diversity of vocal behaviour in polygynous deer is supported by strong anatomical differences, highlighting the importance of anatomical specializations in shaping mammalian vocal repertoires. Sexual selection is discussed as a potential evolutionary driver of the observed vocal diversity and sexual dimorphisms.

In Vitro Evaluation of Biomaterials for Vocal Fold Injection: A Systematic Review

Vocal fold injection is a preferred treatment in glottic insufficiency because it is relatively quick and cost-saving. However, researchers have yet to discover the ideal biomaterial with properties suitable for human vocal fold application. The current systematic review employing PRISMA guidelines summarizes and discusses the available evidence related to outcome measures used to characterize novel biomaterials in the development phase. The literature search of related articles published within January 2010 to March 2021 was conducted using Scopus, Web of Science (WoS), Google Scholar and PubMed databases. The search identified 6240 potentially relevant records, which were screened and appraised to include 15 relevant articles based on the inclusion and exclusion criteria. The current study highlights that the characterization methods were inconsistent throughout the different studies. While rheologic outcome measures (viscosity, elasticity and shear) were most widely utilized, there appear to be no target or reference values. Outcome measures such as cellular response and biodegradation should be prioritized as they could mitigate the clinical drawbacks of currently available biomaterials. The review suggests future studies to prioritize characterization of the viscoelasticity (to improve voice outcomes), inflammatory response (to reduce side effects) and biodegradation (to improve longevity) profiles of newly developed biomaterials.

The effect of nasal septum deviation on voice aging

PURPOSE

The aging process of the voice differs among individuals, and the factors that affect age-related changes in voice are not well-defined. In this study, we investigated the difference between older people with nasal septum deviation (NSD) and older people without NSD in terms of degree of aging voice using objective and subjective voice assessment tools.

METHODS

The study included 94 patients (47 women, 47 men) aged >65 years. Nasal septum deviation was determined in 45 patients (NSD group), and 49 patients had no nasal pathology (control group). Maximum phonation time (MPT), GRBAS scale, and acoustic voice analysis parameters were compared between the NSD and control groups; sub-group analysis disaggregated by sex was also performed.

RESULTS

No significant difference was observed between the NSD and control groups with respect to MPT, GRBAS scale, and acoustic voice analysis parameters in the total study population and among male subjects. The only parameter that showed a significant difference between sub-groups of female subjects was soft phonation index (SPI) (p=.03).

CONCLUSIONS

To the best of our knowledge, this is the first study to analyze the effect of NSD on the voice aging. With the findings of the present study, NSD does not seem to have an effect on voice aging, and also it can be suggested that septoplasty will not have an effect on preventing presbyphonia. Further studies on larger groups of patients are required to provide more definitive evidence on this subject.

Live long and active: Polypeptide-mediated assembly of antibody variable fragments

Antibodies possess multiple biologically relevant features that have been engineered into new therapeutic formats. Two examples include the adaptable specificity of their variable (Fv) region and the extension of plasma circulation times through their crystallizable (Fc) region. Since the invention of the single chain variable fragment (scFv) in 1988, antibody variable regions have been re-engineered into a wide variety of multifunctional nanostructures. Among these strategies, peptide-mediated self-assembly of variable regions through heterologous expression has become a powerful method to produce homogenous, functional biomaterials. This manuscript reviews recent reports of antibody fragments assembled through fusion with peptides and proteins, including elastin-like polypeptides (ELPs), collagen-like polypeptides (CLPs), albumin, transmembrane proteins, leucine zippers, silk protein, and viruses. This review further discusses the current clinical status of engineered antibody fragments and challenges to overcome.

Porcine Vocal Fold Lamina Propria-Derived Biomaterials Modulate TGF-β1-Mediated Fibroblast Activation in Vitro

The vocal fold lamina propria (VFLP), one of the outermost layers of the vocal fold (VF), is composed of tissue-specific extracellular matrix (ECM) proteins and is highly susceptible to injury. Various biomaterials have been clinically tested to treat voice disorders (e.g., hydrogels, fat, and hyaluronic acid), but satisfactory recovery of the VF functionality remains elusive. Fibrosis or scar formation in the VF is a major challenge, and the development and refinement of novel therapeutics that promote the healing and normal function of the VF are needed. Injectable hydrogels derived from native tissues have been previously reported with major advantages over synthetic hydrogels, including constructive tissue remodeling and reduced scar tissue formation. This study aims to characterize the composition of a decellularized porcine VFLP-ECM scaffold and the cytocompatibility and potential antifibrotic properties of a hydrogel derived from VFLP-ECM. In addition, we isolated potential matrix-bound vesicles (MBVs) and macromolecules from the VFLP-ECM that also downregulated smooth muscle actin ACTA2 under transforming growth factor-beta 1 (TGF-β1) stimulation. The results provide evidence of the unique protein composition of the VFLP-ECM and the potential link between the components of the VFLP-ECM and the inhibition of TGF-β1 signaling observed in vitro when transformed into injectable forms.

Magnetic resonance imaging quantification of dehydration and rehydration in vocal fold tissue layers

Clinicians commonly recommend increased hydration to patients with voice disorders. However, effects on clinical voice outcome measures have been inconsistent. Hydration-induced change within different layers of vocal fold tissue is currently unknown. Magnetic Resonance Imaging (MRI) is a promising method of noninvasively measuring water content in vocal folds. We sought to image and quantify changes in water content within vocal fold mucosa and thyroarytenoid muscle after dehydration and rehydration. Excised porcine larynges were imaged using proton density (PD) weighted MRI (1) at baseline and (2) after immersion in one of five hypertonic, isotonic, or hypotonic solutions or in dry air. Larynges dehydrated in hypertonic solutions or dry air were rehydrated and imaged a third time. Scans revealed fluid-rich vocal fold mucosa that was distinct from muscle at baseline. Baseline normalized signal intensity in mucosa and muscle varied by left vs. right vocal fold (p < 0.01) and by anterior, middle, or posterior location (p < 0.0001). Intensity changes in the middle third of vocal fold mucosa differed by solution after immersion (p < 0.01). Hypertonic solutions dehydrated the middle third of mucosa by over 30% (p < 0.001). No difference from baseline was found in anterior or posterior mucosa or in muscle after immersion. No association was found between intensity change in mucosa and muscle after immersion. After rehydration, intensity did not differ by solution in any tissue, and was not different from baseline, but post-rehydration intensity was correlated with post-immersion intensity in both mucosa and muscle (p < 0.05), suggesting that degree of change in vocal fold water content induced by hypertonic solutions ex vivo persists after rehydration. These results indicate that PD-MRI can be used to visualize large mammalian vocal fold tissue layers and to quantify changes in water content within vocal fold mucosa and thyroarytenoid muscle independently.

De Novo Synthesis of Elastin by Exogenous Delivery of Synthetic Modified mRNA into Skin and Elastin-Deficient Cells

Elastin is one of the most important and abundant extracellular matrix (ECM) proteins that provide elasticity and resilience to tissues and organs, including vascular walls, ligaments, skin, and lung. Besides hereditary diseases, such as Williams-Beuren syndrome (WBS), which results in reduced elastin synthesis, injuries, aging, or acquired diseases can lead to the degradation of existing elastin fibers. Thus, the de novo synthesis of elastin is required in several medical conditions to restore the elasticity of affected tissues. Here, we applied synthetic modified mRNA encoding tropoelastin (TE) for the de novo synthesis of elastin and determined the mRNA-mediated elastin synthesis in cells, as well as ex vivo in porcine skin. EA.hy926 cells, human fibroblasts, and mesenchymal stem cells (MSCs) isolated from a patient with WBS were transfected with 2.5 μg TE mRNA. After 24 hr, the production of elastin was analyzed by Fastin assay and dot blot analyses. Compared with untreated cells, significantly enhanced elastin amounts were detected in TE mRNA transfected cells. The delivered synthetic TE mRNA was even able to significantly increase the elastin production in elastin-deficient MSCs. In porcine skin, approximately 20% higher elastin amount was detected after the intradermal delivery of synthetic mRNA by microinjection. In this study, we demonstrated the successful applicability of synthetic TE encoding mRNA to produce elastin in elastin-deficient cells as well as in skin. Thus, this auspicious mRNA-based integration-free method has a huge potential in the field of regenerative medicine to induce de novo elastin synthesis, e.g., in skin, blood vessels, or alveoli.

Nonlinear viscoelastic characterization of human vocal fold tissues under large-amplitude oscillatory shear (LAOS)

Viscoelastic shear properties of human vocal fold tissues were previously quantified by the shear moduli (G' and G″). Yet these small-strain linear measures were unable to describe any nonlinear tissue behavior. This study attempted to characterize the nonlinear viscoelastic response of the vocal fold lamina propria under large-amplitude oscillatory shear (LAOS) with a stress decomposition approach. Human vocal fold cover and vocal ligament specimens from eight subjects were subjected to LAOS rheometric testing with a simple-shear rheometer. The empirical total stress response was decomposed into elastic and viscous stress components, based on odd-integer harmonic decomposition approach with Fourier transform. Nonlinear viscoelastic measures derived from the decomposition were plotted in Pipkin space and as rheological fingerprints to observe the onset of nonlinearity and the type of nonlinear behavior. Results showed that both the vocal fold cover and the vocal ligament experienced intercycle strain softening, intracycle strain stiffening, as well as shear thinning both intercycle and intracycle. The vocal ligament appeared to demonstrate an earlier onset of nonlinearity at phonatory frequencies, and higher sensitivity to changes in frequency and strain. In summary, the stress decomposition approach provided much better insights into the nonlinear viscoelastic behavior of the vocal fold lamina propria than the traditional linear measures.

The Ability of Human Nasal Inferior Turbinate-Derived Mesenchymal Stem Cells to Repair Vocal Fold Injuries

Objective This study investigated the ability of implanted human nasal inferior turbinate-derived mesenchymal stem cells (hTMSCs) to repair injured vocal folds. To this end, we used quantitative real-time polymerase chain reaction (PCR) to analyze the early phase of wound healing and histopathological analysis to explore the late phase of wound healing in xenograft animal models. Study Design Prospective animal study. Setting Research laboratory. Subjects and Methods The right-side lamina propria of the vocal fold was injured in 20 rabbits and 30 rats. Next, hTMSCs were implanted into half of the injured vocal folds (hTMSC groups). As a control, phosphate-buffered saline (PBS) was injected into the other half of the injured vocal folds (PBS groups). Rat vocal folds were harvested for polymerase chain reaction (PCR) at 1 week after injury. Rabbit vocal folds were evaluated endoscopically and the larynges harvested for histological and immunohistochemical examination at 2 and 8 weeks after injury. Results In the hTMSC group, PCR showed that hyaluronan synthase ( HAS) 1, HAS 2, and transforming growth factor ( TGF)-β1 were significantly upregulated compared with the PBS group. Procollagen type III ( COL III) messenger RNA expression was significantly upregulated in the PBS group compared with the normal group. Histological analyses showed that hTMSC administration afforded more favorable collagen and hyaluronic acid deposition than was evident in the controls. Implanted hTMSCs were observed in injured vocal folds 2 weeks after implantation. Conclusions Our results show that hTMSCs implantation into injured vocal folds facilitated vocal fold regeneration, with presenting antifibrotic effects.

Response of an ovine laryngeal injury model to a novel fibrosis inhibitor

BACKGROUND

Vocal fold injury results in severe voice alteration that limits occupational function and social interaction. An ovine model of laryngeal injury has been developed, validated and utilized to examine laryngeal wound healing and the effect of a novel collagen inhibitor (halofuginone) on surgical wound healing. The study design includes basic research and animal model.

METHODS

An ovine laryngeal model was utilized to study controlled vocal fold injury and healing. Twenty-five sheep were divided into five groups. Sheep underwent right vocal fold injury preceded or followed by administration of halofuginone orally, topically or intralesionally. Biopsies were taken at commencement, 1 month and larynges explanted at 3 months. Specimens were examined for elastin and collagen density and epithelial changes. Pearson correlation statistics and Student's t-tests were used to assess inter-relationships.

RESULTS

All sheep tolerated halofuginone. One sheep death occurred in an untreated sheep. Vocal fold tissue demonstrated a predictable histological response to injury. Elastin was significantly reduced post-injury in the glottis. Halofuginone administered orally for 10 weeks prevented elastin loss and demonstrated a trend of reducing collagen density post-injury.

CONCLUSION

In an ovine laryngeal injury model, administration of a fibrosis inhibitor resulted in altered elastin and collagen deposition after injury in the glottis. Further investigation is warranted to examine whether these tissue changes affect vocal fold dynamics.

Tissue engineering-based therapeutic strategies for vocal fold repair and regeneration

Vocal folds are soft laryngeal connective tissues with distinct layered structures and complex multicomponent matrix compositions that endow phonatory and respiratory functions. This delicate tissue is easily damaged by various environmental factors and pathological conditions, altering vocal biomechanics and causing debilitating vocal disorders that detrimentally affect the daily lives of suffering individuals. Modern techniques and advanced knowledge of regenerative medicine have led to a deeper understanding of the microstructure, microphysiology, and micropathophysiology of vocal fold tissues. State-of-the-art materials ranging from extracecullar-matrix (ECM)-derived biomaterials to synthetic polymer scaffolds have been proposed for the prevention and treatment of voice disorders including vocal fold scarring and fibrosis. This review intends to provide a thorough overview of current achievements in the field of vocal fold tissue engineering, including the fabrication of injectable biomaterials to mimic in vitro cell microenvironments, novel designs of bioreactors that capture in vivo tissue biomechanics, and establishment of various animal models to characterize the in vivo biocompatibility of these materials. The combination of polymeric scaffolds, cell transplantation, biomechanical stimulation, and delivery of antifibrotic growth factors will lead to successful restoration of functional vocal folds and improved vocal recovery in animal models, facilitating the application of these materials and related methodologies in clinical practice.

Recombinant Resilin-Based Bioelastomers for Regenerative Medicine Applications

The outstanding elasticity, excellent resilience at high-frequency, and hydrophilic capacity of natural resilin have motivated investigations of recombinant resilin-based biomaterials as a new class of bio-elastomers in the engineering of mechanically active tissues. Accordingly, here the comprehensive characterization of modular resilin-like polypeptide (RLP) hydrogels is presented and their suitability as a novel biomaterial for in vivo applications is introduced. Oscillatory rheology confirmed that a full suite of the RLPs can be rapidly cross-linked upon addition of the tris(hydroxymethyl phosphine) cross-linker, achieving similar in situ shear storage moduli (20 k ± 3.5 Pa) across various material compositions. Uniaxial stress relaxation tensile testing of hydrated RLP hydrogels under cyclic loading and unloading showed negligible stress reduction and hysteresis, superior reversible extensibility, and high resilience with Young's moduli of 30 ± 7.4 kPa. RLP hydrogels containing MMP-sensitive domains are susceptible to enzymatic degradation by matrix metalloproteinase-1 (MMP-1). Cell culture studies revealed that RLP-based hydrogels supported the attachment and spreading (2D) of human mesenchymal stem cells and did not activate cultured macrophages. Subcutaneous transplantation of RLP hydrogels in a rat model, which to our knowledge is the first such reported in vivo analysis of RLP-based hydrogels, illustrated that these materials do not elicit a significant inflammatory response, suggesting their potential as materials for tissue engineering applications with targets of mechanically demanding tissues such as vocal fold and cardiovascular tissues.

Electrospun fiber constructs for vocal fold tissue engineering: effects of alignment and elastomeric polypeptide coating

Vocal fold lamina propria extracellular matrix (ECM) is highly aligned and when injured, becomes disorganized with loss of the tissue's critical biomechanical properties. This study examines the effects of electrospun fiber scaffold architecture and elastin-like polypeptide (ELP4) coating on human vocal fold fibroblast (HVFF) behavior for applications toward tissue engineering the vocal fold lamina propria. Electrospun Tecoflex™ scaffolds were made with aligned and unaligned fibers, and were characterized using scanning electron microscopy and uniaxial tensile testing. ELP4 was successfully adsorbed onto the scaffolds; HVFFs were seeded and their viability, proliferation, morphology and gene expression were characterized. Aligned and unaligned scaffolds had initial elastic moduli of ∼14 MPa, ∼5 MPa and ∼0.3 MPa, ∼0.6 MPa in the preferred and cross-preferred directions, respectively. Scaffold topography had an effect on the orientation of the cells, with HVFFs seeded on aligned scaffolds having a significantly different (p<0.001) angle of orientation than HVFFs cultured on unaligned scaffolds. This same effect and significant difference (p<0.001) was seen on aligned and unaligned scaffolds coated with ELP4. Scaffold alignment and ELP4 coating impacted ECM gene expression. ELP4 coating, and aligned scaffolds upregulated elastin synthesis when tested on day 7 without a concomitant upregulation of collagen III synthesis. Collectively, results indicate that aligned electrospun scaffolds and ELP4 coating are promising candidates in the development of biodegradeable vocal fold lamina propria constructs.

Cyclic tensile strain on vocal fold fibroblasts inhibits cigarette smoke-induced inflammation: implications for Reinke edema

OBJECTIVES

To investigate whether patients with Reinke edema are more extrovertive than patients with carcinoma and, whether cyclic tensile strain (CTS) attenuates cigarette smoke condensate (CSC)-induced inflammation in human vocal fold fibroblasts (HVFF).

STUDY DESIGN

In vitro and ex vivo study.

METHODS

Clinical investigation and Eysenck personality questionnaire were performed to evaluate the personality and smoking status in individuals among groups. 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay was applied to test the viabilities of cultured HVFF exposed to CSC and/or CTS. The messenger RNA (mRNA) and protein expressions of cluster of differentiation 44 (CD44), cyclooxygenase-2 (COX-2), and matrix metalloproteinase-9 (MMP-9) in tissues from Reinke edema, paracancerous site, normal vocal fold, and in HVFF with different treatments were measured by reverse transcriptase polymerase chain reaction or western blot, respectively.

RESULTS

Patients with either Reinke edema or carcinoma were moderate/heavy smokers; the extraversion score, however, was higher in Reinke edema patients than that in carcinoma patients. CD44 mRNA and protein expressions were significantly higher, whereas, COX-2 and MMP-9 expressions were significantly lower in Reinke edema tissues than those in paracancerous tissues. Treatment of HVFF with CSC led to the decrease in cell viability, the reduction in CD44 expression, but, the increase in COX-2 and MMP-9 expressions and, moreover, administration of CTS inhibited such effects of CSC on HVFF.

CONCLUSIONS

Our results demonstrate that Reinke edema patients have more extrovert personality characteristics in comparison to carcinoma patients and, importantly, CTS attenuates CSC-induced inflammation in HVFF. Phonatory vibration may be a mechanism for lower expression of proinflammatory mediators in Reinke edema tissues in spite of cigarette smoke exposure.

Construction and characterization of a novel vocal fold bioreactor

In vitro engineering of mechanically active tissues requires the presentation of physiologically relevant mechanical conditions to cultured cells. To emulate the dynamic environment of vocal folds, a novel vocal fold bioreactor capable of producing vibratory stimulations at fundamental phonation frequencies is constructed and characterized. The device is composed of a function generator, a power amplifier, a speaker selector and parallel vibration chambers. Individual vibration chambers are created by sandwiching a custom-made silicone membrane between a pair of acrylic blocks. The silicone membrane not only serves as the bottom of the chamber but also provides a mechanism for securing the cell-laden scaffold. Vibration signals, generated by a speaker mounted underneath the bottom acrylic block, are transmitted to the membrane aerodynamically by the oscillating air. Eight identical vibration modules, fixed on two stationary metal bars, are housed in an anti-humidity chamber for long-term operation in a cell culture incubator. The vibration characteristics of the vocal fold bioreactor are analyzed non-destructively using a Laser Doppler Vibrometer (LDV). The utility of the dynamic culture device is demonstrated by culturing cellular constructs in the presence of 200-Hz sinusoidal vibrations with a mid-membrane displacement of 40 µm. Mesenchymal stem cells cultured in the bioreactor respond to the vibratory signals by altering the synthesis and degradation of vocal fold-relevant, extracellular matrix components. The novel bioreactor system presented herein offers an excellent in vitro platform for studying vibration-induced mechanotransduction and for the engineering of functional vocal fold tissues.

Classification for animal vocal fold surgery: resection margins impact histological outcomes of vocal fold injury

OBJECTIVES/HYPOTHESIS

Extent of vocal fold injury impacts the nature and timing of wound healing and voice outcomes. However, depth and extent of the lesion created to study wound healing in animal models vary across studies, likely contributing to different outcomes. Our goal was to create a surgery classification system to enable comparison of postoperative outcomes across animal vocal fold wound-healing studies.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Rats underwent one of three types of unilateral vocal fold surgeries classified by depth and length of resection. The surgeries were: for subepithelial injury, resection of epithelium and superficial layer of the lamina propria at the midmembranous portion of the vocal fold; for transmucosal injury, resection of epithelium and lamina propria; and for transmuscular injury, resection of epithelium, lamina propria, and superficial portion of the vocalis muscle. Wound healing was evaluated histologically at various time points up to 35 days postinjury.

RESULTS

Complete healing occurred by 14 days postsurgery for subepithelial injury, and by day 35 for transmucosal injury. Injury remained present at day 35 for transmuscular injury.

CONCLUSIONS

Timing and completeness of healing varied by extent and depth of resection. Scarless healing occurred rapidly following subepithelial injury, whereas scarring was observed at 5 weeks after transmuscular injury. The proposed classification system may facilitate comparison of surgical outcomes across vocal fold wound-healing studies.

LEVELS OF EVIDENCE

N/A.

Characterization of extracellular matrix proteins during wound healing in the lamina propria of vocal fold in a canine model: a long-term and consecutive study

The characterization of vocal fold wound healing can be reflected by the changes of extracellular matrix (ECM) proteins in the lamina propria. Although the expression of ECM proteins after vocal fold injury has been widely studied, such observations have lacked time continuity and integrity of marker proteins. In this study, we observed the morphology of injured vocal folds in a canine model. We used immunofluorescence staining to evaluate the expression and distribution of ECM proteins, such as collagen, elastin, hyaluronic acid, decorin and fibronectin, from 15 days to 6 months after injury. The results showed that large amounts of ECM proteins were secreted 15-40 days after injury. Collagen and fibronectin secretion increased significantly, and were disorderly deposited. The secretion of decorin and elastin increased slightly, while hyaluronic acid decreased. The 15-40 day post-injury period may be the critical intervention stage in wound healing of vocal folds. From 3 to 6 months after injury, the secretion of ECM proteins declined. However, collagen and fibronectin secretion were still significantly higher than normal with irregular arrangement, while the secretion of elastin, hyaluronic acid and decorin decreased significantly at 6 months. This led to vocal fold inelasticity and stiffness, which required effective long-term interventions to treat scar formation.

Study of extracellular matrix in vocal fold biomechanics using a two-phase model

The extracellular matrix (ECM) of the vocal fold tissue consists primarily of fibrous and interstitial proteins. The purpose of this study was to investigate the effects of selective enzymatic digestion of two ECM proteins, namely elastin and versican, on the elasticity of rabbit vocal fold tissue. Quasi-static, sinusoidal, uniaxial tensile tests were performed. The data were analyzed within the framework of a model of the ECM as a two-phase composite material consisting of collagen fibrils as the reinforcing fibers and noncollagenous ECM proteins as the matrix. To validate the two-phase model, the regression parameters for the fibers' volume fraction and shear modulus in a different animal model were compared with corresponding published data. The proposed model was then used to analyze rabbit vocal fold tissues. The mean value and the standard deviation of the fiber volume fraction were found to be 8.49 ± 3.75 % for the control samples (n = 4), 0.59 ± 1.13 % after elastin removal (n = 4), and 8.22 ± 1.06 % after versican removal (n = 4). The results suggest that elastin removal may lead to a reduction in tissue stiffness, through counteracting the reinforcement of collagen fibrils.

Microstructure characterization of a decellularized vocal fold scaffold for laryngeal tissue engineering

OBJECTIVES/HYPOTHESIS

One potential treatment for vocal fold injury or neoplasia is to replace the entire vocal fold with a tissue-engineered scaffold. This scaffold should ideally have similar mechanical properties and extracellular matrix composition as the native vocal fold. As one approach toward this goal, we decellularized human vocal folds and characterized their mechanical properties and extracellular matrix microstructure.

STUDY DESIGN

Basic science investigation.

METHODS

Human vocal folds were dissected from the laryngeal framework and treated with sodium dodecyl sulfate (SDS) to remove all cells. Mechanical properties were measured by indentation before and after SDS treatment. The extracellular matrix components of collagen, laminin, elastin, and hyaluronic acid were also characterized before and after decellularization using histology and immunofluorescence.

RESULTS

After 4 days of SDS treatment, we obtained a scaffold that retained the original geometry of the vocal fold but was devoid of cells. The elastic modulus of the vocal folds did not change significantly before and after decellularization. Upon qualitative inspection, the decellularized vocal folds retained the original collagen, elastin, and laminin content and orientation but lost the original hyaluronic acid.

CONCLUSIONS

Vocal folds can be decellularized using SDS without adversely affecting its mechanical stiffness and fibrous extracellular matrix. This preliminary study demonstrates the potential of a decellularized scaffold to serve as a tissue-engineered construct for vocal fold replacement.

Dynamic vibration cooperates with connective tissue growth factor to modulate stem cell behaviors

Vocal fold disorders affect 3-9% of the U.S. population. Tissue engineering offers an alternative strategy for vocal fold repair. Successful engineering of vocal fold tissues requires a strategic combination of therapeutic cells, biomimetic scaffolds, and physiologically relevant mechanical and biochemical factors. Specifically, we aim to create a vocal fold-like microenvironment to coax stem cells to adopt the phenotype of vocal fold fibroblasts (VFFs). Herein, high frequency vibratory stimulations and soluble connective tissue growth factor (CTGF) were sequentially introduced to mesenchymal stem cells (MSCs) cultured on a poly(ɛ-caprolactone) (PCL)-derived microfibrous scaffold for a total of 6 days. The initial 3-day vibratory culture resulted in an increased production of hyaluronic acids (HA), tenascin-C (TNC), decorin (DCN), and matrix metalloproteinase-1 (MMP1). The subsequent 3-day CTGF treatment further enhanced the cellular production of TNC and DCN, whereas CTGF treatment alone without the vibratory preconditioning significantly promoted the synthesis of collagen I (Col 1) and sulfated glycosaminoglycans (sGAGs). The highest level of MMP1, TNC, Col III, and DCN production was found for cells being exposed to the combined vibration and CTGF treatment. Noteworthy, the vibration and CTGF elicited a differential stimulatory effect on elastin (ELN), HA synthase 1 (HAS1), and fibroblast-specific protein-1 (FSP-1). The mitogenic activity of CTGF was only elicited in naïve cells without the vibratory preconditioning. The combined treatment had profound, but opposite effects on mitogen-activated protein kinase (MAPK) pathways, Erk1/2 and p38, and the Erk1/2 pathway was critical for the observed mechano-biochemical responses. Collectively, vibratory stresses and CTGF signals cooperatively coaxed MSCs toward a VFF-like phenotype and accelerated the synthesis and remodeling of vocal fold matrices.

Modulating the behaviors of mesenchymal stem cells via the combination of high-frequency vibratory stimulations and fibrous scaffolds

We are interested in the in vitro engineering of artificial vocal fold tissues via the strategic combination of multipotent mesenchymal stem cells (MSCs), physiologically relevant mechanical stimulations, and biomimetic artificial matrices. We have constructed a vocal fold bioreactor that is capable of imposing vibratory stimulations on the cultured cells at human phonation frequencies. Separately, fibrous poly (ɛ-caprolactone) (PCL) scaffolds emulating the ligamentous structure of the vocal fold were prepared by electrospinning, were incorporated in the vocal fold bioreactor, and were driven into a wave-like motion in an axisymmetrical fashion by the oscillating air. MSC-laden PCL scaffolds were subjected to vibrations at 200 Hz with a normal center displacement of ∼40 μm for a total of 7 days. A continuous (CT) or a 1 h-on-1 h-off (OF) regime with a total dynamic culture time of 12 h per day was applied. The dynamic loading did not cause any physiological trauma to the cells. Immunohistotochemical staining revealed the reinforcement of the actin filament and the enhancement of α5β1 integrin expression under selected dynamic culture conditions. Cellular expression of essential vocal fold extracellular matrix components, such as elastin, hyaluronic acid, and matrix metalloproteinase-1, was significantly elevated as compared with the static controls, and the OF regime is more conducive to matrix production than the CT vibration mode. Analyses of genes of typical fibroblast hallmarks (tenascin-C, collagen III, and procollagen I) as well as markers for MSC differentiation into nonfibroblastic lineages confirmed MSCs' adaptation of fibroblastic behaviors. Overall, the high-frequency vibratory stimulation, when combined with a synthetic fibrous scaffold, serves as a potent modulator of MSC functions. The novel bioreactor system presented here, as a versatile, yet well-controlled model, offers an in vitro platform for understanding vibration-induced mechanotransduction and for engineering of functional vocal fold tissues.

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.